Elastomers for use in rotary regenerator assemblies are known, e.g., see U.S. Pat. No. 4,148,354 which is herein hereby incorporated by reference. These assemblies comprise ceramic core surrounded by steel ring gear with elastomer therebetween. The elastomer accommodates differential rates of expansion during assembly and during operation.
Materials proposed in U.S. Pat. No. 4,148,354, while satisfactory, do have certain deficiencies. For example, the materials do not function optimally for as long periods as might be desired.
A particularly acute problem is that these materials tend to degrade during extended high temperature service. Others have proposed certain filled organosiloxane and other organic polymers for use in making articles that resist degradation when exposed to extreme conditions. See, for example, U.S. Pat. Nos. 3,098,836; 3,255,152; 3,274,145; 3,506,607; 3,676,420; 3,746,662; 3,791,998; 3,865,784; 3,867,315; 3,911,045; 4,025,485; and 4,069,083.
These patents show that desirable properties may result by loading certain organic polymers with inorganic particulate. It has been discovered in accordance with this invention that besides enhancing certain physical properties as well as potentially reducing material costs, certain particulates also offer improved thermal stability. Improved thermal stability is insufficient by itself, however, to provide a more acceptable material for applications as ring gear assemblies. Rather, such improved thermal stability, when provided by increased particulate loading, is accompanied typically by higher initial viscosities and shorter working times. The higher initial viscosities and shorter working times can make such materials undesirable for high volume production use.
Graphite and certain carbon blacks have been previously suggested for use in combination with certain organopolysiloxanes (see, for example, U.S. Pat. Nos. 3,184,427; 3,399,082; 3,968,055; 3,970,504; 3,969,310 and 4,020,014. U.S. Pat. No. 3,184,427, however, differs with respect to the polymers used and makes no suggestion that graphite may improve high temperature stability of elastomers of this invention. U.S. Pat. Nos. 3,968,055 and 3,970,504 suggest use of a temporary dispersing agent while U.S. Pat. No. 3,399,082 suggests use of graphite in thin emmissive layers. U.S. Pat. No. 3,969,310, on the other hand, suggests use of graphite particulate in dipping or potting application. Finally, U.S. Pat. No. 4,020,014 relates to hot air, peroxide cured compositions with carbon blacks.
As compared to elastomers of commonly assigned U.S. Ser. No. 109,446 and U.S. Ser. No. 109,445 filed concurrently herewith in the names of Theodore et al and Theodore, respectively, the elastomers of this invention, surprisingly, generally have higher thermal conductivity and do not advance hardness as greatly during accelerated aging. Moreover, as compared to elastomers of commonly assigned U.S. Ser. No. 109,439, filed concurrently herewithin the name of Theodore and Lemieux, the elastomers of this invention additionally provide economic advantage.
It is an object of this invention to provide elastomers with improved thermal stability.
It is an object of this invention to provide elastomers with improved thermal stability and whose precursors have desirable initial viscosities and working times.
It is an additional object of this invention to provide elastomer precursors for filling difficult to fill mold cavities.
It is even a still further object of this invention to provide improved elastomer for use in rotary regenerators comprising ceramic core surrounded by steel or other metal ring gear.
These and other objects have been accomplished with elastomers made in accordance with the hereinafter disclosed invention.